Method and apparatus for deposition of particles on surfaces

ABSTRACT

A deposition system is used for depositing particles onto a substrate, such as a wafer in a deposition chamber. The particles are carried in an aerosol that is generated an atomizer that includes an impaction plate for removing large particles before the aerosol is discharged, and which has an output that is provided through a particle classifier to the deposition chamber. Various branches of flow lines are used such that the aerosol that has classified particles in it, is mixed with a clean dry gas prior to discharge into the deposition chamber, and selectively the aerosol can be directed to the deposition chamber without having the particles classified. The lines carrying the aerosol can be initially connected to a vacuum source that will quickly draw the aerosol closely adjacent to the deposition chamber to avoid delays between deposition cycles.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a method and apparatus fordeposition of particles on surfaces, wherein the particles are providedfrom an aerosol generation device that regulates the droplet size andconcentration provided to the deposition chamber so that precisely sizedparticles or spheres are deposited on the surface.

[0002] Pneumatic atomizers are often used for generating aerosolscontaining polystyrene latex (PSL) spheres or particles, as well asother particles, For subsequent deposition on substrates, such assemiconductor wafers. The particles are first suspended in liquid suchas deionized water to form a suspension. The suspension is then atomizedto form droplets. When the droplets evaporate, the PSL spheres orparticles become airborne particles. The generation rate of PSL spheresor particles is a function of droplet generation rate of the atomizerand the probability for a droplet to contain PSL spheres or particles.

[0003] The droplets produced by a pneumatic atomizer normally have abroad size distribution ranging from less than 0.1 μm to larger than 10μm. Large droplets have a high probability to contain more than one PSLsphere or particle. If a droplet contains more than one PSL sphere orparticle, it is called a multiplet. Multiplets provide more PSLparticles than those wanted.

[0004] A droplet that does not contain any particles is called an emptydroplet. When an empty droplet evaporates, it forms a residue particleresulted from the precipitation of nonvolatile impurities dissolved inthe atomizing solution. For example, to prepare a PSL suspension,surfactant is often used to keep suspended PSL spheres from coagulating.The surfactant is one of the sources for residue particles. The size ofresidue particles depends on the size of the droplets and theconcentration of nonvolatile impurities in the atomizing solution. At agiven concentration of the nonvolatile impurity, the residue particlesize is linearly proportional to the droplet size.

[0005] For PSL or particle deposition, the multiplets and the residueparticles are always unwanted. Special atomizers will minimize theformation of multiplets and the size of residue particles by removinglarge size droplets.

SUMMARY OF THE INVENTION

[0006] The present invention relates to a system for depositingparticles on surfaces, in particular semiconductor wafers. The inventioninsures that there is a minimal amount of unwanted material deposited onthe wafer, and that each droplet of the aerosol contains only one sphereor particle. Residues are minimized, and the deposit is uniformly made.

[0007] The present invention, in one aspect, provides for an atomizerthat will atomize droplets that are only within a particular size range,and will insure that the droplets from the atomizer are of size so theywill contain only one particle of the desired material that is going tobe deposited. In this way, empty droplets are avoided, and multiplets,that is, a droplet that contains more than one particle, are alsoavoided.

[0008] A differential mobility analyzer, which can be adjusted to emitonly the particles that are of proper size, is utilized for insuring onesize particle.

[0009] Various forms of devices are included for checking the density ofthe particles in the aerosol and the flow rate. The flow lines permitadding clean gas to the flow of the aerosol as needed, and apre-deposition sequence permits the aerosol flow to be established at ajunction adjacent to the deposition chamber and then switched to thedeposition chamber. The procedure reduces the time between depositioncycles.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a schematic representation of a wafer deposition systemmade according to the present invention;

[0011]FIG. 2 is a flow diagram illustrating the control of the gas thatis used in the atomization process;

[0012]FIG. 3 is a schematic sectional view of a atomizer arrangementused with the present invention;

[0013]FIG. 4 is a vertical sectional view of a differential mobilityanalyzer used in the present invention;

[0014]FIG. 5 is a schematic diagram showing two differential mobilityanalyzers used to broaden the size range of particles that can beprocessed;

[0015]FIG. 6 is a schematic diagram of the aerosol flow lines adjacentthe deposition chamber; and

[0016]FIG. 7 is a schematic representation of connections of a particlecounter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Referring to FIG. 1, a schematic diagram of an entire waferdeposition system is illustrated generally at 10, and includes anaerosol generator or atomizer section 11, which will provide an aerosolalong a line 12 to a differential mobility analyzer 13, that classifiesthe aerosol particles according to size and passes the classifiedparticles along a line system 14 to a deposition chamber illustratedgenerally at 15. Chamber 15 is used for depositing particles carried inthe aerosol onto a wafer. Deposition chambers are well known in the art.A fluid flow through the lines is provided by the positive pressure atthe aerosol generator and by a vacuum pump. Vacuum pump 16 is not usedto evacuate the deposition chamber, but is used to establish initialflow in the lines and through a particle counter.

[0018] The individual sections have valves, flow controllers, pressureregulators, and the like as will be explained in connection with theindividual sections.

[0019]FIG. 2 illustrates the atomizer section 11. A source of clean drygas 17 provides the gas through a pressure regulator 18, a mass flowcontroller 19, and a three way valve 21 to an atomizer indicatedgenerally at 20. The mass flow controller 19 controls the mass flow fromthe pressure regulator 18 to the atomizer 20 The flows are balanced andclean gas can be added to and mixed with the atomizer output.

[0020] As shown in FIG. 3, atomizer 20 has a body 23 with an air or gasinlet passageway 23A from the flow controller 18. The flow passesthrough an orifice 23D into an atomization chamber or nozzle 23B intowhich an atomizing liquid 23L from a container is drawn. The liquid isbroken up into droplets in chamber or nozzle 23B. An impaction plate 22is installed adjacent to but spaced from the outlet of the atomizernozzle 23B to remove large droplets by impaction. The impaction plate 22can be an annular band or wall, if desired.

[0021] Three parameters for determining the output droplet size andvolume are dimensions of the orifice or passageway 23D between inletpassageway 23A and atomizer nozzle 23B, the diameter of the nozzle 23B,and the distance from the outlet opening of nozzle 23B and the impactionplate 22. The diameter of orifice 23D is identified as D1 and indicatedby arrows 24, the diameter of the output nozzle 23B is identified as D2and indicated by arrows 26. The distance from the nozzle 23B outlet tothe impaction plate surface is identified as D3 and indicated by arrows28. Atomizing orifice 23D controls the total atomizing gas flow. When D1is constant, reducing dimension D2, the outlet diameter of the nozzle23B, and reducing dimension D3, the distance from the nozzle outlet tothe impaction plate surface, will result in a smaller output dropletsize. By selectively changing D2 and D3, the size of the dropletsproduced by the atomizer can be regulated. The droplet size is selectedso each droplet will contain one PSL particle. The PSL particles arealso regulated in size, and the goal of no empty droplets and nomultiplets can be achieved. With different types of particles, this goalalso can be achieved by appropriate sizing of the orifice 23D, theatomizing nozzle 23B, and the distance from the nozzle to the impactionplate.

[0022] The aerosol produced from the atomizer 20 of FIG. 3, and otheratomizers, consists of droplets carried in a saturated gas, usually air.One way to evaporate the droplets is to mix the aerosol droplets withdry gas or air. Referring to FIG. 2, the clean dry gas from source 17and mass flow controller 19 splits into two streams at a junction 30.The atomizing gas flows into the 3-way valve 21. A mixing gas flow isdiverted from a junction 30 along a line 32, through a mixing flowcontrol comprising an orifice 34 One port of the 3-way valve 21 isselectively connected to the inlet of atomizer 20 and the other port ofvalve 27 is selectively connected to a bypass line 38 which hasbalancing flow control orifice 40. The output lines from the atomizer,line 32, and line 38 join at junction 20J.

[0023] During aerosol generation, the 3-way valve 21 is connected to theinlet passage 23A of the atomizer 20, producing aerosol droplets. Theaerosol droplets then mix with a controlled volume of clean dry air/gasfrom the mixing flow control orifice 34. If the atomizer 20 is to beshut off, the valve 21 directs flow through balancing flow controlorifice 40.

[0024] The flow from 3-way valve 21 through the inlet passage 23A,orifice 23D and nozzle 23B of the atomizer 20 produces the aerosoldroplets by aspirating liquid containing PSL particles (or otherparticles) from the liquid and particle source 23L. The aerosol dropletsthen mix with clean dry air or other gas provided at a junction 20J fromthe mixing flow control. After mixing, the droplets will evaporate,forming an aerosol of PSL spheres or particles for deposition. One wayto control the three flows, that is, the aerosol flow, the mixing flowand balancing flow is using properly sized orifices. The control orifice34 for the mixing flow, the orifice 23D for the atomizing flow and theorifice 40 for the balancing flow are sized such that at a givenpressure of the clean dry gas or air, the total flow through the aerosolgenerator to line 41 is a constant regardless of whether the 3-way valve21 provides the input flow to the atomizer for atomizing liquid or tothe balancing flow control orifice. The atomizing flow is shut off whenthe valve 21 is moved to provide flow to the line 38.

[0025] The output from the atomizer in line 41, goes through a 3-wayvalve 42. The valve 42 can divert the aerosol along a line 42A thatbypasses the size classification. The normal operating position of valve42 will transmit the aerosol to a junction 41J (see FIG. 1) in the line12 where the desired flow goes to the differential mobility analyzer 13.

[0026] The line 12 has a flow control orifice 44 in the line, as well asa charge neutralizer 46, which will de-ionize the aerosol, and reduceelectrical charges from the particles. The line 12 is branched atjunction 41J to line 48, that passes through a filter 50, and a flowcontrol restriction 52. The flow control restriction 52 is illustratedas an orifice, but also could be a mass flow controller. The flowrestriction will control the volume of the aerosol that is divertedthrough the line 48 and through filter 50 as a function of the totalflow and the flow provided to the DMA 13. A pressure sensor 54 is usedfor sensing the pressure in the line 48, and keeping it regulatedappropriately, and a temperature sensor 56 is also utilized. Theseparameters are utilized as feedback for controlling the inputs to theDMA. The line 48 is connected to the sheath flow input to thedifferential mobility analyzer, and provides what is called the DMAsheath flow. The filter 50 removes most of the particles in the aerosol,so the sheath flow is essentially a clean gas.

[0027] The aerosol in the line 12 is injected into the center of theDMA. The DMA will discharge only particles that are of a desired size.The DMA is used to insure that the particles that are to be provided tothe deposition chamber will be only one size or monodisperse.

[0028] The differential mobility analyzer (DMA) 13 is shown in detail inFIG. 4, and it operates to classify particles so that they aremonodisperse particles. The DMA 13 comprises a tubular housing 62through which the divided flow from the atomizer 20 passes and includesthe sheath flow from line 48 as mentioned, as well as the aerosol flowfrom line 12. The aerosol flow, which is indicated by the block 64 inFIG. 4 enters ports 66 in the housing 62 and flows down through anannular passageway 68 formed between the inner surface of housing 62 anda flow distributor 72, which is a sleeve spaced from the outer housingto provide an aerosol flow passageway, and surrounds a central electrode70, which is a tubular electrode. The aerosol flow thus surrounds and isspaced from the tubular central electrode 70. The aerosol flows downalong the outside of the flow distributor sleeve 72, so that it staysalong the inside surface of the housing 62. The sheath flow, indicatedby block 65, from line 12 is introduced through a port 74, and flowsdown through a central passageway 77 of an insulator sleeve 76 that hasa high voltage electrode 78 which is connected to a source of highvoltage and which extends through the central passageway, and connectsto the tubular high voltage electrode 70.

[0029] As the sheath flows down through the passageway 77, it will bedischarged into the interior of the flow distributor 72 and flow downalong the surfaces of the tubular electrode 70 to provide a sheath ofclean air surrounding the electrode. The aerosol particles carrying alow level of electrical charge, as they move from the inlet end 66 ofthe DMA housing 62 to the outlet, the voltage on the electrode 70 is setso the correct size of particles will be attracted to enter an openingshown at 82 in the side wall of the electrode, and then discharge outthrough a central passageway 84 in an end piece 86 of the tubularelectrode 70. The particles of the selected size discharge out through aline 88. The output of the DMA is a monodispersed aerosol, that is, anaerosol with only one size particle. The voltage from the source 80controls the size of the particles that will enter the opening 82, andat a set voltage only one size will pass through the passageway 84 andthe line 88.

[0030] Excess flow and containing particles that are of a different sizefrom that which will pass through the opening 82, are carried outthrough an excess flow passageway 90, and through a filter 90A, a flowcontroller 90B and a line 90C to a desired location.

[0031] The total flow from the aerosol generator 11 can be maintained ata set level, the flow from one outlet of valve 42 is split into two flowstreams, one for the DMA sheath flow and the other comprising apolydisperse aerosol flow to be size-classified by the DMA. The ratio ofthe DMA sheath flow rate to polydisperse aerosol flow rate is controlledby the two flow restrictions 44 and 52 shown in FIG. 1. All theparticles in the DMA sheath flow are removed by filter 50 (which canhave two sections) prior to the flow restriction or flow control device52. The flow restriction or flow control device 52 for the sheath flowcan be an orifice flow restriction or a flow controller such as a massflow controller. The polydisperse aerosol flow in line 12 cannot besatisfactorily controlled by a mass flow controller since the flowcarries a high concentration of particles, some of which would beremoved by a mass flow controller.

[0032] The flow restriction device 34 is an orifice or similar devicethat will restrict the aerosol flow without loss of particles. The ratioof the DMA sheath flow rate to the polydisperse aerosol flow rate isfixed if orifices are used for controlling both DMA sheath flow and thepolydisperse flow. The ratio can be adjusted by adjusting the sheathflow rate with flow control device 52 if it is a flow controller. Thetotal flow through the DMA is kept constant, and the output particlesize is controlled by the voltage of source 80.

[0033] The DMA monodisperse aerosol output flow from DMA 13 that isdirected to line 14 is controlled by orifice 92. The DMA excess flow canbe controlled by an orifice 90B or a flow controller. When using anorifice to control both flows from the DMA, the two orifices areproperly sized to keep a constant ratio of the flow rates in lines 88and 90C. When the DMA excess flow in line in 90C is controlled by a flowcontroller, the ratio of the two flow rates, that is the ratio of flowsin lines 88 and 90C, can be adjusted by adjusting the DMA excess flowwith a flow controller replacing orifice 90B.

[0034] As shown in FIG. 5 two differential mobility analyzers areprovided in a modified embodiment of the invention to widen the sizerange of particles that can be provided in the monodisperse flow to thedeposition chamber. DMA 13 has a long housing and flow path and canclassify particles in a size range from 0.10 to 2.0 μm. An additionalshort housing DMA 136 will classify a range of particles from 0.01 to0.3 μm. The DMA 136 operates in the same manner as DMA 13, except theparts are made to suit the smaller size particles. When combined, theDual-DMA system covers a size range from 0.01 to 2.0 μm.

[0035] To accommodate two DMA's, a 3-way valve 137 is placed in line 48downstream from flow restriction 52. A line 138 is connected to oneoutput of valve 137 and carries the sheath flow to DMA 136 when valve137 is in position to connect line 48 to line 138. The polydisperseaerosol line 12 is branched with a 3-way valve 140 and a connected line142 to the aerosol input of the DMA 136. The DMA 136 is constructed asshown for the DMA 13, but the different length and other known designdimensions results in being operable for the different range of particlesizes.

[0036] The monodisperse outlet line 144 of DMA 136 is connected througha 3-way valve 146 to the output line 88 of DMA 13, upstream from theflow restriction 92. The excess flow from DMA 136 is discharged througha filter 147 and line 148. The excess flow can be discharged as desired.The 3-way valves 137, 140 and 146 can be simultaneously operated by acentral controller 151 when the output from atomizer 11 is providingparticles in the range for the respective DMA. The controller 151 isused to control all the valve flow controllers, pressure regulators andthe like. Feedback from the pressure sensors, temperature sensors andflow sensor are used by central controller 151 to provide the properadjustments.

[0037] As shown in FIG. 1, after the monodisperse flow passes throughflow restrictor or flow control orifice 92, the monodispersed aerosolflow can be mixed at a junction 91 with a clean gas or air, that is fedfrom a junction 97 on the output line 18A of regulator 18 through branchline 94 and 95. Line 94 has an orifice 96, a flow controller 98 and afilter 100 for regulating flow and for removing any particles. Theparticle carrying gas, mixed with the dry clean gas to achieve thecorrect particle density in the flow moves along a line 102. A furtherflow control restrictor 104 is provided. A first 3way valve is providedto selectively direct the flow to a waste line when deposition is notdesired.

[0038] A second 3-way valve 108 in line 102 is used to direct theaerosol flow either to a spot deposition nozzle in a deposition chamber110 along line 111 or to a deposition showerhead along a line 109. Thedeposition chamber 110 can be made as desired. The aerosol is thendeposited onto a wafer in the chamber with the exhaust going through afilter 118. The flow through the deposition chamber 110 is determined bypressure differentials in the lines used.

[0039] If desired, the flow from the output of the valve 108 along lines111 and 109 can be drawn directly to the vacuum pump 16 through a filter114, and an on/off valve 116. When valve 116 is open, flow will passthrough a flow restrictor 119 and then to the low pressure side of thevacuum pump 16. Additional filters can be provided as desired. The line109 from the 3-way valve 108 is coupled into a line 120 which, as shown,is also connected to the output of a pressure regulator 18 through line95, a flow restrictor 126, a flow controller 122, and a filter 124. Anon/off valve 128 provides a bypass around the flow controller 122. Flowrestrictor 126 remains in the flow lines regardless of whether valve 128is on or off.

[0040] The flow from line 95 also can be sent through flow controller122 as a purge flow to purge the deposition chamber with clean dry airor gas.

[0041] If desired, the output aerosol from the atomizer 20 can bediverted by valve 42 along the line 42A to line 120 and thus to thedeposition chamber for direct deposition, without passing the aerosolthrough the DMA. The direct deposition function is normally used fordepositing large size PSL particles (500-4000 nm). In this case, theresidue particles are not of concern since they are normally muchsmaller. Typically, residue particles are smaller than 30 to 50 nm undernormal operating conditions of atomizers presently available.

[0042] Another feature of the present invention is shown in FIG. 6. Theresponse time for the deposition system 10 can be reduced by reducingthe time lag for introducing the aerosol from lines or passages 111 or109 to deposition chamber 110. Prior to deposition, the aerosol is drawnto the close vicinity of the deposition chamber 110 by vacuum fromvacuum pump 16 as controlled by on/off valve 116. The vacuum pump 16 isdesigned such that it will provide a flow that is slightly higher thanthe required deposition aerosol flow. When the valve 116 is turned on(open), the aerosol from any one of the lines 109, 111, or 120 will bepulled from valve 108 and line 109 or line 111 to the exhaust by thevacuum pump 16. In addition, since the vacuum flow rate is slightlyhigher than the desired deposition aerosol flow, there will be a smallreverse flow from the deposition chamber 110, via the deposition nozzle115B or the deposition showerhead 115A (see FIG. 6), to the vacuum pump16 when the valve 116 is turned on. This flow will remove contaminatesfrom the deposition chamber and will cause the respective line 109 or111 (depending on the setting of valve 108) or from line 120 if it isbeing used, to fill with the aerosol down to the junction with lines109A and 111A, connecting the main portions of these lines to valve 116.

[0043] The spot deposition nozzle 115B is connected to line 111 and isfor depositing particles in controlled size spots on a wafer. Thedeposition showerhead 115A is connected to line 109 and is for largerarea deposition, as is well known.

[0044] After valve 116 has been on sufficiently so the line 109 or 111is filled with the desired aerosol and the deposition chamber 110 ispurged by the reverse flow, the on/off valve 116 will be shut off andthe aerosol in either line 109 or line 111 will enter the depositionchamber immediately because of the close coupling of the lines to thechamber and the prefilling of the lines with the correct aerosol. Thedeposition response time is thus significantly improved by providing thepreflow out the vacuum pump 16.

[0045] After each deposition cycle, the valve 116 for the vacuum controlis turned on by central controller 151. The residual particles in thespot deposition nozzle or in the deposition showerhead after eachdeposition will, therefore, be sucked to the vacuum source. Crosscontamination of particles between depositions is avoided.

[0046] Also as shown in FIGS. 1 and 6, orifice 104 is used for flowmeasurement in combination with a differential pressure sensor 105 tomeasure and monitor the deposition flow of mono size aerosol flow inline 102. During deposition, the deposition flow and aerosolconcentration are continuously monitored and the deposition time isdynamically adjusted, based on the measured aerosol concentration anddeposition flow rates.

[0047] A particle counter 160 (FIGS. 1 and 7) which is a condensationnuclei counter (CNC) is used to determine aerosol concentration bycounting the number of particles that pass through the counter when theflow is held at a standard flow rate. The counter input line 162 isconnected to line 102 through line 163 and a valve 164. The particleconcentration can be measured at set intervals or for a set time as eachdeposition cycle starts. The output line from the counter 160 isconnected to vacuum pump 16.

[0048] As shown in FIG. 7, a flow restriction device or orifice 166 in abypass line is used to control the CNC bypass flow. The flow restrictiondevice 166 is sized to have the same flow rate as the CNC 160 samplingflow rate. That is, the flow rate through the line 163, which carriesflow from line 102 to the CNC counter 160 or, when the counter is shutoff, to flow restriction 166, is kept as a constant, whether the valve164 is turned to provide flow to the CNC 160 or turned to provide flowthrough the flow restriction 166. The constant bypass flow through theCNC or restriction 166 helps to maintain the stability of the entiredeposition system during operation. The particle concentration in theaerosol is determined by the CNC operating at a standard flow rate. Anon-off valve 165 can be used to positively stop flow through the CNC160.

[0049] The dynamic adjustment of the deposition time parameter is basedon the measured aerosol concentration from counter 160 and depositionflow rate signals from restriction 104 and pressure sensor 105. Withproper calibration, a very high deposition count accuracy of achieved.For example, a deposition count accuracy of ±3% is achieved, which isthe combination of flow and concentration measurement accuracies.

[0050] The volumetric flow rates of DMA sheath flow, input aerosol flowto the DMA in line 12, the monodisperse aerosol flow in lines 88 and102, and excess flow in line 90 directly affect the sizing accuracy ofthe DMA. If a DMA is calibrated at a certain temperature and pressure,the DMA may not give an accurate sizing response if it is used in anenvironment that has a different ambient temperature and/or pressure.Temperature sensor 56 and pressure transducer 54 measure DMA temperatureand pressure (ambient temperature and pressure, and air/gas temperatureand pressure inside the DMA). The signals from the real-time measurementof temperature and pressure are sent back to the controller 151 forproper compensation to the flow controllers and other variableparameters to ensure the sizing accuracy of the DMA.

[0051] As shown in FIG. 4, the DMA is an instrument that classifiesparticles according to electric mobility of the particles. It can bedescribed as a cylindrical condenser consisting of a metal rodconcentrically located within a metal tube. Polydisperse aerosol andclean sheath air are introduced into the DMA and flow down the annulusbetween the center electrode and the outer tube as laminar streams. Ahigh DC voltage is applied to the center electrode while the outer tubeis grounded. The electric field between the two cylindrical electrodescause charged particles in the aerosol to deflect across the streamlinesto the exit slit near the bottom of the tubular electrode rod. Thevoltage needed to deflect particles to the output air stream is thenrelated to the electric mobility of the particles. The relation betweenthe particle diameter and the required center rod voltage can beobtained using such known equations. In practical use, the voltage isscanned to find the peak voltage corresponding to the maximum particleconcentration in the monodisperse aerosol output stream. The voltage isthen used to calculate the corresponding particle size.

[0052] All size particles other than the selected size from the DMA,including residue particles and multiplets of the PSL spheres, areremoved by electrostatic separation by the DMA. If the atomizing PSLsolution has one PSL peak, the DMA will output the PSL spheres at thepeak size. If the PSL solution contains multiple PSL size peaks, the DMAwill output the peak size PSLs closest to the size specified by theoperator. For example, if four PSL sizes are to be deposited onto awafer, four containers with solutions which each contain one specificPSL sphere size are provided. The four PSL sphere sizes can be mixed anduse the DMA system to output one PSL sphere size at a time fordeposition.

[0053] The DMA system using two DMAs covers the size ranges of 100 to2000 nm. The two DMA systems offer the highest accuracy and resolutionin its size range. The low detection limit of the smaller DMA can beextended to 3 nm.

[0054] Classified deposition particle size, that is, using a mono-sizeaerosol from the output of the DMA, is much preferred for PSL or processparticles smaller than 1000 nm. After being neutralized to remove excesscharges from atomization in neutralizer 46 the aerosol is received bythe DMA and classified by the DMA either by direct classification, orsize distribution scan and classification. In the size distribution scanand classification mode, the aerosol from the atomizer is first scannedto determine the aerosol size distribution and then classified fordeposition. In this operation mode, only the PSL spheres at the peaksize are deposited regardless of the broadness of the originaldistribution of the PSL spheres in the atomizing solution. The PSL sizein this operation mode is referred as the Label Size, which is given bythe PSL sphere manufacturer. For creating Absolute ContaminantStandards, this operation mode is most widely used when United StatesNational Institute of Science and Technology (NIST) or NIST traceablePSL spheres are used for deposition.

[0055] The classification-only operation mode is often preferred byexperienced users. In this mode, the particle size is referred as theDMA size based on the particle's electrical mobility. Since the DMA iscalibrated using NIST standard PSL spheres, the DMA size is in goodagreement with the standard PSL spheres. The DMA has a sizing accuracyof ±2% while PSL spheres from different vendors may have as much as 10%difference in size. The DMA size is, therefore, more accurate than mostLabel Sizes including some NIST traceable PSL spheres.

[0056] The classification-only mode is also referred as the processparticle deposition mode since it is widely used for process particledeposition. In process particle deposition, the original particles inatomization solution normally have a broad size distribution. With theclassification mode of the DMA, the output particles for deposition canbe any size within the original distribution. In this operation mode,the deposition can be made very fast, for example, up to 30 depositionsper hour.

[0057] The chamber 110 has provisions for both spot deposition and fulldeposition. The spot deposition is useful since it can deposit multiplespots of different sizes on a single wafer. Advantages of using multiplespots include reduction in inspection system calibration time and cost,increase in calibration accuracy, improvement in inspection systemperformance and ease of monitoring the contamination level of the Wafer.

[0058] Although the present invention has been described with referenceto preferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

What is claimed is:
 1. A deposition device for depositing particles ontoa substrate surface in a deposition chamber, said particles beingcarried in an aerosol, wherein the improvement comprises an atomizingnozzle for discharging an atomized liquid containing particles formingthe aerosol, and an impaction plate spaced from the atomizing nozzleagainst which the aerosol is impacted, said impaction plate beingpositioned to remove droplets above a selected size prior to dischargeof the aerosol into a fluid stream to be received by the depositionchamber.
 2. The improvement of claim 1, wherein the aerosol isdischarged in a fluid stream carried in a flow line, and a valve in theline for selectively directing the aerosol to a first line and to asecond line, the first line having a differential mobility analyzer toobtain a selected size of particles as a discharge to the depositionchamber.
 3. The improvement of claim 2, wherein the second line providesa discharge of the aerosol directly to the deposition chamber.
 4. Theimprovement of claim 2, wherein the second line has a junction whichdivides the aerosol in the line into two individual flows, the secondline carrying a first flow to the differential mobility analyzer andcarrying particles thereto for classification as to size of particles tothe outlet, and the second flow being carried in a sheath flow linehaving a filter therein for removing particles, and connected to thedifferential mobility analyzer and providing a sheath flow of gas to thedifferential mobility analyzer.
 5. The improvement of claim 1, whereinthe line leading to the differential mobility analyzer has a chargeneutralizer for reducing electrical charges from the aerosol.
 6. Theimprovement of claim 1, wherein the atomizer is provided with a cleangas at an inlet, a junction for diverting a portion of the clean gasthrough a branch line, said branch line connecting to an outlet of thedifferential mobility analyzer, to mix with the output of thedifferential mobility analyzer in a preselected ratio.
 7. Theimprovement of claim 6, wherein said branch line has a flow controllertherein, said flow controller controlling the amount of clean gasintermixed with the output from the differential mobility analyzer.
 8. Awafer deposition system for depositing particles onto a wafer in anenclosed deposition chamber, a source of an aerosol carrying particles,a first line connecting said source of aerosol to said chamber, saidline having a branch line leading to a vacuum pump, said branch linebeing joined to said first line adjacent the deposition chamber, and avalve to direct the flow in the first line to the vacuum pump in a firststate, and in a second state to close the branch line to direct theaerosol to the deposition chamber.
 9. The deposition system of claim 8,wherein the vacuum pump draws a flow through the branch line that isgreater than the flow from the source of aerosol, both the first lineand branch line being connected to the deposition chamber, such thatdeposition chamber is connected to the vacuum pump and air is removedfrom the vacuum chamber when the valve is in its first state.
 10. Thedeposition system of claim 8, wherein said first line carrying theaerosol has a second branch line connected thereto, upstream of thedeposition chamber, said second branch line being selectively connectedto direct flow through a particle counter, to monitor the particlescarried in the aerosol in the first line.
 11. The deposition system ofclaim 8, wherein the source of aerosol comprises an atomizer having anozzle with an outlet, an impaction plate mounted in alignment with thenozzle outlet for removing large particles from the aerosol prior todischarge from the atomizer.
 12. The deposition system of claim 8,wherein said vacuum pump generates a flow of gas greater than the volumeof the flow of the aerosol carried in the first line, said depositionchamber being connected to the first line and to the branch line, suchthat the vacuum pump, when connected to the first line removes gas fromthe deposition chamber as well as from the first line.
 13. Thedeposition system of claim 8, wherein said aerosol is generated from anaerosol generator, said aerosol generator having an output line, and adifferential mobility analyzer for classifying particles in the outputline from the aerosol generator, said differential mobility analyzerpermitting a selected size of particles to be directed through the firstline to the deposition chamber.
 14. The deposition system of claim 13,wherein said flow from said aerosol generator is divided into two flows,a first of the flows being provided to the differential mobilityanalyzer, and a second of said flows having a filter therein forremoving particles and being connected to provide a sheath gas flow inthe differential mobility analyzer.
 15. The deposition system of claim14 and a pressure sensor and a temperature sensor in the line providinga sheath gas flow to the differential mobility analyzer for providingfeedback signals for controlling the differential mobility analyzer. 16.The deposition system of claim 14, wherein said differential mobilityanalyzer comprises an elongated cylindrical tube having an outer wall, acentrally located elongated electrode in said outer wall, a voltageprovided to said electrode, a flow of gas on an interior surface of thedifferential mobility analyzer comprising the sheath gas flow, and anopening in said electrode for receiving particles of a selected sizedependent upon parameters for controlling the differential mobilityanalyzer, said particles being discharged to the deposition chamber. 17.The deposition system of claim 13, wherein there is a seconddifferential mobility analyzer, the second differential mobilityanalyzer being configured to provide particles at a different size rangefrom the first mentioned differential mobility analyzer, and valves forcontrolling the flow of sheath gas and particle carrying aerosolselectively to each of the differential mobility analyzers.
 18. Thedeposition system of claim 10 and a source of a clean gas connected tosaid first line upstream of said particle counter, said clean gas mixingwith the aerosol to provide a desired concentration of particles asdetermined by the particle counter.
 19. The deposition system of claim18, wherein said source of clean gas is selectively connected through aflow controller directly to the deposition chamber for providing apurging flow through the deposition chamber.
 20. The deposition systemof claim 18, wherein the first line has a flow measurement deviceinstalled therein for determining the flow of aerosol to the depositionchamber.
 21. The deposition system of claim 10, wherein the first lineleading to the deposition chamber has a third branch line there, saidthird branch line being connected to a vacuum source, an on-off valve inthe third branch line for coupling the vacuum source to the first lineat selected times, said vacuum source drawing aerosol into the firstline and to the vacuum source when the valve is open to precharge thefirst line with aerosol to be discharged into the deposition chamber.